The present invention is directed to a self-cutting, undercutting dowel formed of an anchor rod and a sleeve laterally enclosing the anchor rod. The anchor rod has a head part leading in the setting direction of the dowel and with an increasing diameter in the setting direction. The leading end of the sleeve is divided by slots into expansion sections. When the sleeve is driven over the head part, the expansion sections are flared radially outwardly. At least one of the expansion sections has a cutting edge for abrasively cutting the receiving material into which the dowel is inserted for forming an undercut.
In fastening techniques, frequently it is necessary to produce fastening elements largely free of expansion pressure. In particular, when edge and axial distances are small, there is the danger that cracking or chipping of the receiving material will take place in anchors or fastening elements using conventional expansion dowels. In such situations, anchoring systems are known in which a special fastening element is anchored positively in an accommodating borehole. The accommodating borehole is provided, at a defined depth, with an undercut. The fastening element inserted into the prepared accommodating borehole is formed of an anchor rod with a head part leading in the setting direction and which head part has an increasing diameter in the setting direction, and a sleeve forming a bore which is placed axially over the anchor rod. The leading end of the sleeve has sections which can be flared outwardly into the undercut by displacing the sleeve relative to the anchor rod.
In most cases, special equipment is needed to form the undercut and such equipment has an abrasive cutting edge which rotates eccentrically in the accommodating borehole so that the undercut is milled into the wall of the borehole. There are known undercutting dowels which automatically produce an undercut during the setting procedure. Such a self-cutting, undercutting dowel or anchor is described in U.S. Pat. No. 4,702,654 and includes a sleeve with expansion sections at its leading end in the setting direction extending from a plastic joint towards a conically shaped expanding head part at the leading end of the anchor rod. The expansion sections can be flared radially outwardly by displacing the sleeve over the head part, which is supported at the base of the borehole. The expansion sections are equipped with pin-shaped cutting edges inserted into the outer surface of the expansion sections. When the sleeve is rotated, the cutting edges, which overlap the circumference of the sleeve, form an undercut in the wall of the borehole at the same time that the expansion sections are flared radially outwardly. The setting procedure of the undercutting dowel is completed when the sleeve has traversed the necessary axially extending path and the expansion sections have been flared to the desired extent.
The setting of this known self-cutting, undercutting dowel is achieved with the help of a rotary percussion drill for driving the sleeve axially and rotating it relative to the expanding head part on the anchor rod. In such known undercutting dowels, the driving or percussion component of the drill is not used very effectively in forming the undercut. As a result, the cutting procedure is prolonged and it may happen that the expansion sections of the undercutting dowel are not fully expanded. In particular, contact with reinforcing bars can have an adverse effect on the formation of the undercut causing a negative effect on the desired holding values. Moreover, the cutting pins, inserted into the outer surface of the expansion sections, can become loose and fall out due to the high axial stress resulting from the axial impacts of the drill during the setting procedure.